Steerable sheath with variable curve span

A shaft assembly, comprising:

• (a) a proximal section extending distally along a longitudinal axis of the shaft assembly, the proximal section comprising a proximal shaft defining a proximal lumen;
• (b) a distal section extending distally from the proximal section, the distal section comprising a distal shaft defining a distal lumen configured to align with the proximal lumen of the proximal shaft, the distal section being configured to be biased to deflect laterally away from the longitudinal axis of the shaft assembly into a deflection curvature having a width, the distal section being configured to fit within a cardiovascular anatomical passageway;
• and
• (c) a stiffener member assembly comprising a collar, and a first stiffener member attached at one end of the first stiffener member to an outer wall of the collar, the stiffener member assembly configured to selectively translate in a direction of the longitudinal axis such that the collar translates within the proximal lumen or the distal lumen and the first stiffener member translates within a first side lumen in the proximal shaft and the distal shaft, the first side lumen being off-axis relative to the proximal lumen and the distal lumen, the first stiffener member being configured to counteract the lateral bias of the distal section and thereby reduce the width of the deflection curvature based on a longitudinal position of the first stiffener member relative to the distal section.